(1) Field of the Invention
The present invention relates to a content distributing technique for transmitting and receiving content between devices connected to a home network, and particularly to a content-log analyzing technique for use in distributing content.
(2) Description of the Related Art
In recent years, the business of distributing “content” such as movies and music as being recorded on DVDs or CDs, or via the Internet or broadcast satellites has been widespread. Such content distributed from suppliers to users is copyrighted. In view of protecting the copyright, the suppliers are required to manage content so as not to allow the users to use the content beyond the scope of their-license.
The non-patent document 1 discloses a technique relating to DTCP (Digital Transmission Content Protection). The DTCP technique provides a system for mutual authentication between devices connected via the IEEE1394 high-speed serial bus. According to this technique, devices licensed to use content are each given a secret key. When one device intends to transmit or receive content to or from another device, the two devices first perform mutual authentication between them using their secret keys. Then, the device transmits or receives the content to the other device using a shared key resulting from the mutual authentication. Without an authentic license, therefore, a device cannot use content even if it belongs to a home network.
While great many pieces of content are provided to the users, some of them are highly valuable content (high-value content) for which a license that limits the number of copying times or the like is set. Examples of such high-value content include high-quality digital video, and movies released just recently. The suppliers desire to prohibit distribution of high-value content to such devices that may possibly decode and rewrite the license set for the high-value content. For example, a PC (personal computer) obtaining high-value content within a home network may possibly decode and rewrite its license. In such a case, the higher the frequency of the PC obtaining content, the higher the possibility of the PC having the intention to break the copyright protection. Non-patent Document 1: 5C Digital Transmission Content Protection White Paper (Revision 1.0 Jul. 14, 1998)